1. Field of the Invention
This invention relates to a logic circuit using Schottky barrier FETs.
2. Description of the Related Art
The electron mobility of GaAs is several times that of silicon. A logic circuit constructed using GaAs is suitable for a high speed logic processing. The elements made of GaAs have received considerable attention because of their nature that the forward voltage necessary for the logic drive is low, and hence the power dissipation is small. This impels the development of the logic ICs constructed with Schottky barrier FETs.
The logic circuit consisting of GaAs Schottky barrier FETs comes in two varieties, the DCFL (direct coupled FET logic) and the SCFL (source coupled FET logic). The DCFL is made up of a switching element and a load element, both elements being constructed with Schottky barrier FETs. The logic output is derived from the junction point between them. The SCFL is of the current switching type in which a couple of Schottky barrier FETs are differentially connected with each other. One of the attractive features of this type of the logic ICs may be driven usually by approximately 1 V or 2 V.
It is a rare case that a logic system is constructed by using only the logic ICs based on the GaAs Schottky barrier FETs. Most of the logic systems are constructed by using both the GaAs ICs and the silicon ICs such as CMOS and ECL. The silicon based IC usually requires 3 to 5 V for its drive source. This indicates that such logic systems reject use of the same power voltage. One of the measures thus far taken for this is to divide the power voltage for the silicon ICs by resistors, for example, into a voltage suitable for driving the GaAs ICs. This measure, however, creates another problem of increased power dissipation, although it allows use of a single power source for these different types of ICs.